1. Field of the Invention
The present invention relates to an internally meshing planetary gear device wherein a circular arc tooth form is used for an internal gear and an epitrochoid tooth form is used for an outer gear of a planetary gear. More specifically, the present invention relates to useful art for simultaneously achieving high efficiency, low abrasion, low backlash, high loading ability, high rigidity, high precision and excellent control ability in a planetary gear device of such a type.
The present invention is aimed to enhance efficiency of a motion control device for an indexing device of a machine tool, an industrial robot or the like, or a servo actuator.
2. Description of Related Art
In conventional indexing devices used for machining center (MC), a combination of an AC servo motor and a worm gear reduction device is mainly used. However, a worm gear reduction device has extremely low efficiency and causes a problem when it is sped up due to a large slip between meshing surfaces and a high pressure at contact surfaces. Further, it also suffers from backlash due to the slip at the gear surfaces, and its efficiency further decreases. In order to avoid backlash, an adjusting mechanism is necessary, and maintenance of such an adjusting mechanism is troublesome.
Contrary to this, in addition to the worm gear reduction device, there are internally meshing planetary gear devices, wherein a circular arc tooth form is used for an internal gear, and wave gear devices, both of which are widely used at articulations of industrial robots, by which high reduction ratio can be obtained easily.
For example, Japanese Utility Model Publication No. Sho 61-16439 discloses an internally meshing planetary reduction device wherein an internal gear has a circular arc tooth comprising pins and rollers and an outer gear has a trochoid tooth form, characterized in that outer rollers which is longitudinally divided into two are rotatably supported on outer pins which are disposed on the internal surface of an annular frame which forms a housing of internal gear, and an intermediate supporting portion for supporting the outer pin is formed between the outer rollers which are longitudinally spaced from each other by a small distance.
Further, Japanese Utility Model laid-open No. Sho 58-102855 discloses an eccentric swing type reduction device comprising a case having internal teeth in a pin shape, a support block which is rotatable relative to the case, a pinion which has outer teeth meshing with the internal teeth and which performs eccentric revolution, and an eccentric crank mechanism which is disposed on the support block and which activates the pinion, characterized in that both ends of the pins are rotatably supported on the case by means of rolling bearings.